In gas turbine engines a turbine operated by combustion product gases drives a compressor which furnishes air to a burner. Gas turbine engines operate at relatively high temperatures, and the capacity of such an engine is limited to a large extent by the ability of the turbine blades to withstand the thermal stresses that develop at such relatively high operating temperatures. The ability of the turbine blades to withstand such thermal stresses is directly related to the materials from which the blades are made, and the material's strength at high operating temperatures.
A turbine blade includes a root portion at one end and an elongated blade portion which extends from the root portion. A platform extends outwardly from the root portion at the junction between the root portion and the blade portion. To enable higher operating temperatures and increased engine efficiency without risk of turbine blade failure, hollow, convectively cooled turbine blades are frequently utilized.
Such turbine blades generally have intricate interior passageways which provide torturous, multiple pass flow paths to assure efficient cooling that are designed with the intent that all portions of the turbine blades may be maintained at relatively uniform temperature. However, due to the centrifugal and boundary layer effects on the cooling air as it flows through the interior passageways, areas of the turbine blade which should be convectively cooled may be inadequately cooled. This inadequate cooling can result in local "hot spots" in the turbine blade where the turbine blade material is exposed to temperatures that can damage the turbine blade so as to significantly reduce the useful life of the turbine blade. If such a hot spot should occur in the blade portion of the turbine blade adjacent the root portion of the blade near the blade platform, cracks can begin to develop at the hot spot.
During engine operation, high stresses occur in the turbine blade at the junction of the blade portion and the root portion, and in particular at the trailing edge of the blade portion due to the relatively small thickness of the blade portion at that location. Any crack that occurs in the trailing edge near the root portion may propagate rapidly across the blade portion during engine operation, liberating the blade portion of the turbine blade. A blade portion so liberated can lead to severe damage, or in some cases destruction, of the engine.
What is needed is a turbine blade which prevents such hot spots from developing in the trailing edge of the blade portion at the blade platform.